Why digital grain looks fake, and how to add film grain to iPhone photos

Most grain effects in filter apps, editors and cameras make noise and blend it on top of the photo. At a glance it looks like film. I think of grain as the salt of a film photo. With the right amount, nobody notices it. With the wrong kind, the whole dish tastes of the packet.

What real film grain is

A black-and-white emulsion is gelatine full of tiny silver-halide crystals. Exposure and development turn some of those crystals into specks of metal silver. Where more light fell, more crystals develop, and the negative gets darker. Grain is what you see when those specks are enlarged. There's no smooth tone, only solid specks that light can't pass through, and the specks fall at random.

Colour film starts the same way. Then development forms clouds of dye around each developed crystal, and the silver is bleached out. Colour film has three layers, one each for red, green and blue light. Each layer has its own dye clouds, and the clouds in different layers don't line up. So colour grain changes in colour from speck to speck, as well as in brightness.

Bigger crystals make a faster film, and a faster film has more visible grain. A slow ISO 100 film has small, tight grain. A fast ISO 1600 film has big, rough grain.

Why grain changes with tone

One good way to describe grain in maths is the random disc model. In this model, grains are discs dropped at random places. At each point, the picture depends on how much of that point the discs cover. Newson, Delon and Galerne (2017) used it to build a grain renderer that works at any resolution.

When the discs cover almost nothing, there's almost no randomness to see. When they cover everything, there's almost none either. In between, the random changes are at their biggest. So the strength of grain depends on the tone, and one layer on top can't copy that.

Film makers measure this too. Kodak's data sheets give a grain number called RMS granularity. It's read through a 48-micrometre opening, at a density the sheet names. The sheet has to name a density, because the number changes with density (see the Double-X technical data and Wikipedia on film grain).

Five signs of fake grain

• One layer at one strength. The same noise sits on a black shadow, a grey wall and a white sky. Film never does that.
• Grey noise on a colour picture. It looks like a screen in front of the photo.
• Too sharp and too even. Noise made of single pixels is crisp and even. Film grain forms spots. Each spot has a size and soft edges, and the spots gather in uneven groups.
• The wrong order. If grain goes on before sharpening, the sharpening makes it harsh and crunchy. If it goes on before noise reduction or resizing, those steps smooth it away.
• The wrong scale. Grain that looks right at full size disappears when the photo is made smaller for a phone screen. Grain sized for a small preview looks like gravel at full size.

How to add film grain to iPhone photos

• Make it follow tone. Strongest in the middle tones, still there in bright areas, and fading to nothing at pure black and pure white.
• Give it a size as well as an amount. Mix a fine and a coarse layer of noise to make spots instead of static. The spot size is also called the grain's correlation size.
• Use colour grain on colour photos. Separate grain for red, green and blue copies the three emulsion layers. Black-and-white looks get grey grain.
• Add it last. Put it after the develop, tone, colour and your own edits, so sharpening and noise reduction can't touch it.
• Size it by format and speed. Faster film has bigger crystals, and a smaller frame is enlarged more for a print of the same size. So 16 mm cine film looks gritty, and large formats look almost clean.

RAW or HEIF for grain

A HEIF from the iPhone has already been through noise reduction and sharpening. Those steps smear fine detail into the painterly look people complain about. If you put grain over that, you get grain on top of watercolour. A RAW keeps the sensor's own texture, so grain looks most like film on RAW. The trade-offs and file sizes are in iPhone RAW vs HEIF for a film look. Plain RAW in the dark can be noisy, and that noise can fight with the grain. Then clean up the sensor noise a little first.

Other grain tools

Lightroom's grain has Amount, Size and Roughness (Adobe's help page). Roughness makes the grain less even. On the iPhone 18 Pro, Apple added a Grain control to Photographic Styles. PetaPixel's review says it's only on or off, so you can't change how much grain it adds. The review also says it works on HEIF only, without RAW.

How much grain is right

Use less than you think, then a bit less again.

• Match the grain to the light. Bright daylight and slide-film looks need fine grain. Night, flash and dark rooms can take a lot more, because that's when film photographers loaded fast film.
• Judge it at the size people will see it. Instagram shows photos about 1080 pixels wide. To shrink a 12 or 48 megapixel photo to that size, each new pixel is the average of the pixels next to it. That averaging removes most of the fine grain. For a feed, raise the grain's size a little instead of its amount.
• Export at full resolution. Then the app you post to makes the photo smaller once, instead of twice.
• Check at 100%. Zoom in on the photo. If the grain is the first thing you notice, you've salted the plate instead of the food.
• Pair it with the rest of the stock. Heavy grain on a clean picture with strong contrast looks like noise. On a soft, film-like tone with a little halation, it looks like film.
• Don't add grain on top of grain. A second app's grain doubles the first, at two different sizes. Start from a file with no edits.

In Chobial

Grain is part of each film, under Effects. It's soft noise in small spots, with a coarser second layer on top. Colour films get a little grain in colour, and black-and-white films get neutral grain. Its size is set for a 12 megapixel photo and scaled to the size of the saved photo. So the grain on the screen is the grain you get in the file.

Grain goes on after the film's tone, colour and Strength dial, because it belongs to the stock. Your edits don't sharpen it.

• Load a film with the grain you like. Many built-in films have their own grain, and about 20 have none. Press has gritty press-photo grain, and Night has heavy grain. Dusk has coarse pushed grain, and Vintage has heavy grain with soft detail. For fine grain, try Vivid or Lifelike. Mono has no grain at all. Swipe across the picture to change the film, and you see its grain live in the viewfinder.
• Let the ISO do some of the work. Every film has a box speed. Gold is rated at 200, and Portrait and B&W at 400. The rest are rated by how much grain they have, like real film. Shoot faster than the box speed, and the grain gets stronger and slightly coarser with each stop, up to three stops. That's what pushing a roll does. At or below the box speed, the film keeps its own grain.
• Change it on one photo. In the Library, open the photo, tap Edit, choose the Film tool and slide Grain. The slider starts at the film's own amount. The photo develops again from its original.
• Build your own grain. In Films, tap + › New Film and choose a film to Start From. Open Effects and pick a Grain Stock. Then slide Grain (the amount, 0 to 100%) and Size (0.5 to 3). Tap the checkmark to save.

Each Grain Stock sets both sliders, and you can move them afterwards:

The films work on ProRAW, RAW, HEIF and JPEG. For noisy RAW at night, a film's Develop section has its own noise reduction. The app exports at full resolution unless you pick a smaller size. For the rest of the look, see how to make iPhone photos look like film and how the films are made.